At least 11 migrants died at sea and another 263 were rescued on Sunday in two separate operations off the coast of Libya, the country's navy said.

In the first operation, "a coastguard patrol... was able to rescue 83 illegal migrants and recovered 11 bodies in a rubber boat five nautical miles northeast of Sabratha," navy spokesman General Ayoub Kacem told AFP.

Sabratha is about 70km west of Tripoli.

"The 11 dead migrants drowned when the dinghy overturned but were recovered by the survivors and hoisted into the boat," said Mohamad Erhouma, a member of the nearby city of Zawiyah's coastguard.

The second rescue operation took place off the coast of Zliten in the country's east, where 180 migrants were rescued from two boats, according to General Kacem.

The migrants, of different African nationalities, "were aboard two inflatable boats when they were intercepted and then brought back to the port of Tripoli," he said.

Since the 2011 fall and killing of longtime leader Muammar Gaddafi, Libya has become a key launch pad for migrants making desperate bids to reach Europe, often on unseaworthy vessels.

Sharp drop from July

More than 600,000 have crossed the central Mediterranean to Italy in the past four years, the vast majority embarking from Libya.

Since last July there has been a sharp drop in crossings as Libyan authorities backed by Italy pressured local groups to stop smuggling and supported Libya's coastguard to intercept those who do leave.

European powers have also pushed to reduce flows into Libya from the south and the International Organization for Migration (IOM) has flown back 25,000 migrants from Libya to their home countries since the start of last year.

About 5,330 migrants had crossed from Libya to Italy between 1 January and 20 April, 85 percent lower than during the same period in 2017, according to Italy's interior ministry.

Last year alone, 3,116 people died attempting the crossing, according to the IOM, including 2,833 sailing from Libya.